Carbon fibers produced from polyacrylonitrile (PAN), a pitch, etc., have hitherto been used chiefly for their mechanical characteristics, but have recently been reappraised as high performance material. For example, application of carbon fibers as electromagnetic shielding or as synthetic electric wires utilizing a graphite interlaminar compound has been studied.
Upon consideration of the application of such carbon fibers as high performance material, a PAN carbon fiber, included under the category of sparingly graphitizable carbon, achieves poor development of a graphite structure even when subjected to high temperature treatment. Carbon fibers produced from a mesophase pitch are regarded as superior in graphitizing properties to those of the PAN carbon fiber, but are still unsatisfactory as compared with graphite, since the mesophase pitch is obtained from coal tar or residual oil and is not uniform in the structure of its constituting compounds. For example, Japanese Patent Publication No. 4287/85 teaches that a graphitized fiber having an electrical resistivity of from 150.times.10.sup.-6 to 200.times.10.sup.-6 .OMEGA.cm can be obtained by heat treatment of a carbon fiber prepared from a mesophase pitch at 3000.degree. C. This result is inferior to that of a graphite fiber prepared from a carbon fiber grown in a vapor phase, i.e., 65.times.10.sup.-6 .OMEGA.cm, which is believed attributable to the non-uniform structure of the compounds constituting the mesophase pitch used as a starting material.
On the other hand, the carbon fibers grown in a vapor phase which are now attracting attention as fibrous graphite show satisfactory development of a graphite structure as described above and are expected to be applied as functional material. Nevertheless, they are produced as having a fiber length of only several centimeters and, therefore, have their own limit of application. Moreover, their production yield is low.